The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
Not applicable.
(1) Field of the Invention
The present invention relates to a transducer for steering parametric mode acoustic beams. More specifically, the present invention relates to an apparatus comprised of a plurality of elements apodized from a conductive material and arranged over a piezoelectric continuum surface to direct an acoustic beam at a desired frequency and steering angle.
(2) Description of Prior Art
It is practiced in the art to dispose four electrically phased signals (0, 90, 180, 270 degrees) through an array of piezoelectric elements over a piezoelectric continuum surface to direct an acoustic beam at a desired frequency and steering angle such as described in U.S. Pat. No. 6,108,275 to Hughes et al. This conventional, or non-parametric, configuration operates in the linear mode. In a linear mode, changing the frequency results in a change to the steering angle.
In general, if an array contains N-by-N elements, the number of independent control points required for broadband beam steering equally in two dimensions is N2. As used herein, xe2x80x9cbeam steeringxe2x80x9d refers to directing acoustic energy from a moving surface in a desired direction, usually by varying the amplitude and phase of the individual parts of the surface in a systematic manner over the surface. Beam xe2x80x9csteering anglexe2x80x9d is the angle at which acoustic energy is directed relative to the face of the transducer. Because the number of control points increases as the square of piezoelectric elements in any of two orthogonal directions comprising the array, the complexities of fabrication and control of the array similarly increase with the addition of elements. Because conventional, linear mode, low frequency sources require very large radiating apertures to form directional acoustic beams, they often require a large number of elements and the attendant cost and complexity that goes with them.
What is therefore needed is an apparatus for directing an acoustic beam comprised of piezoelectric elements that has a relatively small radiating aperture, can be easily and affordably fabricated, and which requires few control points to operate an array of piezoelectric elements.
Accordingly, it is an object of the present invention to provide a transducer apparatus for steering wideband parametric mode acoustic beams.
In accordance with the present invention, a piezoelectric embedded monolithic active surface for transmitting a directed acoustic beam comprises a monolithic active surface, a plurality of piezoelectric elements formed on said surface by the apodization of a continuous conductor forming an array of electrodes comprising, a plurality of coupled frequency pairs comprising, a first primary frequency row extending in a frequency steered direction the first primary frequency row comprising means for accepting a first primary frequency signal, and a second primary frequency row extending in the frequency steered direction and located adjacent to the first primary frequency row the second primary frequency row comprising means for accepting a second primary frequency signal, wherein the plurality of coupled frequency pairs repeat in a delay-steered direction and wherein each of the coupled frequency pairs comprises a means for accepting a time delayed copy of the first and second primary frequency signals.